To continue adding transistors to integrated circuits without significantly increasing die sizes, the distance between transistors and other devices may have to be reduced. The need to reduce the distance between devices may require reducing the width of the landing area for the contacts. As a result, when contact is made to the landing area, part of the contact may extend laterally over the isolation structure, forming a borderless contact. To prevent the contact etch step from etching into the isolation structure, an etch stop layer may be formed on the surface of the device prior to performing the contact etch. Such a layer may comprise silicon nitride.
Processes that add such an etch stop layer require extra steps, e.g., an extra nitride layer deposition step and a two step contact etch. Moreover, where such a nitride etch stop layer is formed over a silicide, the nitride must be deposited at a relatively low temperature to maintain junction and silicide integrity. Depositing nitride using a low temperature process may, however, adversely affect a device's reliability. In addition, when a relatively thick nitride layer is used to form the etch stop, e.g., to ensure the contact etch will not completely remove that layer, that layer may require devices to be spaced further apart. Requiring additional spacing to accommodate a thick nitride layer may diminish the reduced spacing benefit that borderless contacts may otherwise provide.
Accordingly, there is a need for a method for making borderless contacts that either eliminates altogether the need to form a silicon nitride etch stop layer after silicide formation, or allows for the use of a thinner nitride etch stop layer.